The present invention relates to a cigarette manufacturing machine with an auxiliary tobacco feed unit. Cigarette manufacturing machines are known to be made comprising an input chamber from which shredded tobacco is drawn off by a carding unit and fed to a downward duct. At the bottom end of the latter, provision is made for a supply conveyor for feeding the tobacco towards the bottom end of an upward output duct.
Generally speaking, the said downward duct, which is never without a column of tobacco inside, also acts as a store, the tobacco being drawn off continually from the bottom end of the duct by a toothed roller which feeds it on to the said conveyor.
Known cigarette manufacturing machines of the aforementioned type are usually partly supplied with recirculated tobacco collected downstream from the said upward output duct, by means of skimming devices, and frequently fed straignt back into the said input chamber.
Owing to the small size of the recirculated tobacco particles and, consequently, the difficulty encountered by the carding unit in collecting them, such a solution does not always guarantee a sufficiently uniform level of tobacco inside the downward duct.
This lack of uniformity involves a number of major drawbacks in that it results in an uneven stream of tobacco being formed by the said toothed roller on the said conveyor and, consequently, in uneven distribution of the tobacco along the continuous cigarette rod formed at the output of the said upward duct.
In an attempt to overcome this drawback, recirculated tobacco is known to be fed straight into the downward duct, a number of level detectors being arranged over the width of the latter for detecting the height of the said column at different points. The signals supplied by the said detectors are used for controlling the supply of recirculated tobacco into the said downward duct, so as to ensure the tobacco level is maintained constant over the entire width of the said downward duct.
For example, recirculated tobacco is known to be supplied essentially crosswise in relation to the axis of the said downward duct, by means of a rocking tray designed to turn round an axis parallel with that of the said downward duct. The said tray is provided with an outlet smaller in width than the said duct and designed to shift in response to the said signals, so as to supply recirculated tobacco wherever needed to keep the height of the column even.
As the said outlet describes an arc of a circle as it travels over the width of the said downward duct, using the aforementioned rocking tray entails using downward ducts of relatively ample size crosswise in relation to width.
In other words, the aforementioned rocking tray entails using a large-section downward duct the size of which in view of the duct's additional function, already mentioned, of storing the tobacco, is invariably such as to compress the tobacco inside the duct and impair uniform distribution of the same on the said supply conveyor.